Moving components of engines, such as pistons, cylinders, and rocker arms, often are fabricated from hypereutectic alloys of aluminum and silicon. These hypereutectic alloys typically contain in the range of from about 16% to about 23% by weight silicon--an amount that is far beyond the solid solubility level for the silicon in the alloy. As a result, excess silicon tends to precipitate as angular particles generally about 10 microns in size. After the component is manufactured, an electrochemical etch typically is used to remove some of the aluminum matrix at the surface of the component. The etch causes precipitated silicon particles to protrude from the matrix, forming a hard bearing surface.
Bearing surfaces comprising these protruding silicon particles frequently are in frictional contact with a metallic counterfacing surface, such as a chromium-plated piston ring, a steel rocker shaft, or a component made of some other ferrous alloy, such as cast iron. Frictional wear between these counterfacing surfaces remains a serious problem.
The problem is exacerbated by "oil starvation." Current attempts to reduce hydrocarbon emissions from engines often involve the use of less lubricating oil. The resulting "oil starvation" can cause increased wear on the load-bearing surfaces. If increased wear persists, oil can seep past the ring. The result is wear-related hydrocarbon emissions which defeat the purpose of using less lubricating oil in order to reduce emissions.
Methods are needed to alter the load-bearing surfaces to promote the effectiveness of conventional lubricants in preventing tribochemical attrition of silicon and metal.